This invention relates to weight measuring and value computing apparatus and more particularly to improved apparatus for weighing, computing a value and printing an article label showing the weight, price per unit weight and computed value of each of a plurality of successive articles. The apparatus includes a novel scale no motion detector for detecting when a measured weight is constant for a predetermined time interval.
In recent years the demand for increased efficiency has created the need for high speed measuring apparatus capable of automatically weighing successive articles and, for each weighed article, computing a value based upon a predetermined price per unit weight and printing an article label bearing such weight, price per unit weight and computed value. Such measuring apparatus is commonly used, for example, in supermarket meat departments. After a butcher cuts and divides meat into package portions, the meat may be automatically packaged and subsequently labeled by automatic weight measuring, value computing and label printing apparatus.
In the past, apparatus for weighing an article, computing an article price and printing an article label have included a combination of mechanical, optical and electrical elements. A typical prior art system of this type is described in U.S. Pat. No. 3,384,193 which issued on May 21, 1968 to William C. Susor et al. and U.S. Patent 3,453,422 which issued on July 1, 1969 to William C. Susor. This system includes a mechanical-optical scale which generates a digital signal corresponding to an article weight. A computer multiplies the measured weight by a price per unit weight, using a partial products method of multiplication, to obtain the article's value. The measured weight data, the price data and the computed value data are then supplied to a printer for producing an article label. The system is provided with various interlocks which reduce the chances of printing erroneous labels or multiple labels for a single article. For example, if the price per unit weight or the tare weight data are changed, a "lock" switch must be manually pushed to prevent accidental changes in this data. A label cannot be printed if the weight or the computed value exceed the capability of the system. After a label is printed, another interlock prevents printing the next label until the printed label is removed from the printer for application to the article. The system includes a scale no motion detector which inhibits computing an article value and printing a label until the measured weight reaches a steady state.
Although systems of this type have been extremely successful, there has been a need for faster-operating and more accurate systems. The prior systems generally have included mechanical-optical devices for performing the weight measurement and for motion detection. One method for detecting motion involves either rotating a disc or moving a mask through a distance proportional to the weight on the scale. One or more photodetectors sense the presence and absence of slots on the disc or of lines on the mask for detecting motion. However, the sensitivity of systems of this type varies with the position of the disc or mask with respect to the photodetector. If an edge of a slot or line is adjacent the photodetector, very small vibrations may cause an indication of motion, even though the measured weight remains substantially constant. If the disc or mask is positioned such that the photodetector senses in the center of a slot or line or in the center of the region between two adjacent slots or lines, the sensitivity of the motion detector is at a minimum. Here the sensitivity may be so small that the scale output can change without any indication of motion.